1. Field of the Invention
The present invention relates to a metal-resin composite including a hollow or solid metal internal member, a hollow metal external member within which the internal member is disposed, and an intermediate layer disposed between the internal member and the external member, and to a method for producing the metal-resin composite.
2. Description of the Related Art
PCT Japanese Translation Patent Publication No. 2001-507647 discloses a known automotive body structure. The automotive body structure has a tube-in-tube structure including an internal tube whose surface is coated with a resin-based single layer, and an external shell. This structure allows the beam to have an extremely high stiffness without increasing the weight. The resin-based layer contains a bubble forming agent that may contain either a chemical foaming agent or a physical foaming agent. When the matrix of the resin-based layer is a thermally curable or thermally expanding resin, the resin-based layer is cured and/or expanded by heating.
For example, an automotive door beam may use a structure including a hollow or solid metal member (hereinafter referred to as first member) disposed within a hollow metal member (hereinafter referred to as second member) made of, for example, steel. The first member is intended for reinforcement.
A foaming resin is foamed during heating (and immediately after heating) to produce a force expanding the entire volume of the resin. After the completion of heating, however, a stage is present where the foaming is stopped and the resin has not yet been cured completely. If a metal-resin composite including the first member and the second member with a resin layer in between is produced, the production process is generally performed in such a manner that the first member and the second member are assembled with their axes extending in the horizontal direction, and the internal first member, during heating, is supported by the expansion force of the entire resin without falling into the resin layer. However, in the above-mentioned stage after heating, the first member falls and is displaced from the intended position because of the softness of the resin layer and the contraction of foam gas. It is however important to accurately position the first member from the viewpoint of strength.
When grooved (not hollow) members are combined with each other and the space between the two members is filled with a resin, as disclosed in PCT Japanese Translation Patent Publication No. 2001-507647, supporting brims provided to both members help align the upper member with the lower member, thus preventing the problem that the upper member falls into the resin. On the other hand, when a metal-resin composite including a hollow or solid first member and a hollow second member with a resin intermediate layer in between is produced, the production process is performed in such a manner that an assemble of the first member and the second member is laid with their exes extending in the horizontal direction, and the first member is not supported by any member. Consequently, the above problem is liable to occur that the first member falls into the soft resin under its own weight in the stage before the resin is cured.
In this instance, the resin may not completely fill a region above the first member, and, thus, a gap or a low-density foamed portion may be formed. The gap or low-density portion causes an insufficient strength of the foamed resin requiring a reinforcing ability.
Also, use of additional positioning members for supporting the first member at both ends is not desirable because the number of parts is increased. Also, if both ends of the first member are closed, such positioning member cannot be used.